<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Calculator Made By @Abhay557</title>
</head>
<style>
*{
    font-family: 'Poppins', sans-serif;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body{
    display:flex;
    justify-content:center;
    align-items:center;
    min-height: 100vh;
    background-color: #233342;
}
.calculator{
    border-radius: 35px;
    background: #233342;
    box-shadow:  26px 26px 35px #1c2834,
             -26px -26px 35px #2a3e50;
    position: relative;
    display:grid;
}

.calculator .value{
    grid-column: span 4;
    height: 70px;
    text-align: right;
    border: none;
    outline:none;
    padding: 10px;
    font-size: 18px;
    border-radius:30px;
    margin: 10px;
}

.calculator span{
    margin: 10px;
    border-radius:50px;
    display:grid;
    width: 60px;
    height: 60px;
    color: #fff;
    background-color: #0c2835;
    place-items: center;
    border: 1px solid rgba(0,0,0,.1);
}

.calculator span:active{
    background: #74ff3b;
    color:#111;
}

.calculator span.clear{
    grid-column: span 2;
    width: 140px;
    background: #e25057;
}

.calculator span.plus{
    grid-row: span 2;
    height: 140px;
}

.calculator span.equal{
    background: #7c4dbe;
}
</style
<body>
    <form class="calculator" name="cal">
        <input class="value" type="text" name="txt" readonly="">
        <span class="num clear" onclick="document.cal.txt.value = ''">C</span>
        <span class="num" onclick="document.cal.txt.value += '/'">/</span>
        <span class="num" onclick="document.cal.txt.value += '*'">*</span>
        <span class="num" onclick="document.cal.txt.value += '7'">7</span>
        <span class="num" onclick="document.cal.txt.value += '8'">8</span>
        <span class="num" onclick="document.cal.txt.value += '9'">9</span>
        <span class="num" onclick="document.cal.txt.value += '-'">-</span>
        <span class="num" onclick="document.cal.txt.value += '4'">4</span>
        <span class="num" onclick="document.cal.txt.value += '5'">5</span>
        <span class="num" onclick="document.cal.txt.value += '6'">6</span>
        <span class="num plus" onclick="document.cal.txt.value += '+'">+</span>
        <span class="num" onclick="document.cal.txt.value += '1'">1</span>
        <span class="num" onclick="document.cal.txt.value += '2'">2</span>
        <span class="num" onclick="document.cal.txt.value += '3'">3</span>
        <span class="num" onclick="document.cal.txt.value += '0'">0</span>
        <span class="num" onclick="document.cal.txt.value += '00'">00</span>
        <span class="num" onclick="document.cal.txt.value += '.'">.</span>
        <span class="num equal" onclick="document.cal.txt.value = eval(document.cal.txt.value)">=</span>
    </form>
    
</body>
</html>
